Using Redis with Node.js

Redis is a fast and efficient in-memory key-value store. It is also known as a data structure server, as the keys can contain strings, lists, sets, hashes and other data structures. If you are using Node.js, you can use the node_redis module to interact with Redis. This tutorial explains various ways of interacting with Redis from a Node.js app using the node_redis library.

Installing node_redis

node_redis, as you may have guessed, is the Redis client for Node.js. You can install it via npm using the following command.

npm install redis

Getting Started

Once you have installed node_redis module you are good to go. Let’s create a simple file, app.js, and see how to connect with Redis from Node.js.

Now, type node app in the terminal to run the app. Make sure your Redis server is up and running before running this snippet.

Storing Key-Value Pairs

Now that you know how to connect with Redis from Node.js, let’s see how to store key-value pairs in Redis storage.

Storing Strings

All the Redis commands are exposed as different functions on the client object. To store a simple string use the following syntax:

client.set('framework', 'AngularJS');

Or

client.set(['framework', 'AngularJS']);

The above snippets store a simple string AngularJS against the key framework. You should note that both the snippets do the same thing. The only difference is that the first one passes a variable number of arguments while the later passes an args array to client.set() function. You can also pass an optional callback to get a notification when the operation is complete:

The above snippet stores a hash in Redis that maps each technology to its framework. The first argument to hmset() is the name of the key. Subsequent arguments represent key-value pairs. Similarly, hgetall() is used to retrieve the value of the key. If the key is found, the second argument to the callback will contain the value which is an object.

Note that Redis doesn’t support nested objects. All the property values in the object will be coerced into strings before getting stored.

The above snippet creates a list called frameworks and pushes two elements to it. So, the length of the list is now two. As you can see I have passed an args array to rpush. The first item of the array represents the name of the key while the rest represent the elements of the list. You can also use lpush() instead of rpush() to push the elements to the left.

To retrieve the elements of the list you can use the lrange() function as following:

Just note that you get all the elements of the list by passing -1 as the third argument to lrange(). If you want a subset of the list, you should pass the end index here.

Storing Sets

Sets are similar to lists, but the difference is that they don’t allow duplicates. So, if you don’t want any duplicate elements in your list you can use a set. Here is how we can modify our previous snippet to use a set instead of list.

This snippet will retrieve all the members of the set. Just note that the order is not preserved while retrieving the members.

This was a list of the most important data structures found in every Redis powered app. Apart from strings, lists, sets, and hashes, you can store sorted sets, hyperLogLogs, and more in Redis. If you want a complete list of commands and data structures, visit the official Redis documentation. Remember that almost every Redis command is exposed on the client object offered by the node_redis module.

Now let’s have a look at some more important operations supported by node_redis.

Checking the Existence of Keys

Sometimes you may need to check if a key already exists and proceed accordingly. To do so you can use exists() function as shown below:

The incr() function increments a key value by 1. If you need to increment by a different amount, you can use incrby() function. Similarly, to decrement a key you can use the functions like decr() and decrby().

Conclusion

We have covered the basic and most commonly used operations in node_redis. You can use this module to leverage the full power of Redis and create really sophisticated Node.js apps. You can build many interesting things with this library such as a strong caching layer, a powerful Pub/Sub messaging system and more. To know more about the library check out their documentation. I hope you enjoyed reading the article. Let us know what you think in comments.